Electric discharge device



June 1955 w. R. BAKER ETAL ELECTRIC DISCHARGE DEVICE 1 Filed Dec. 3, 1946 /NVNTOR5. WILL/AM R. BA KER 7IIIIIIIIIIIIIIIIIIIIIIIIII SAMUEL C. CURRAN 6r ATTORNEY.

ELECTRIC DISCHARGE DEVICE William R. Baker, Berkeley, Calif., and Samuel C. Curran, Glasgow, Scotland; said Baker assignor to the United States of America as represented by the United States Atomic Energy Commission Application December 3, 1946, Serial No. 713,640

18 Claims. (Cl. 250-413) The present invention relates to calutrons and more particularly to apparatus operative to aid in an effect called space charge neutralization.

The detailed construction and operation of a calutron is fully set forth in the copending application of Ernest 0. Lawrence, Serial No. 557,784, filed October 9, 1944. For the purpose of completeness in the present disclosure, the following brief description is given.

A calutron is a device for separating and collecting isotopes of elements and comprises essentially an evacuated tank or vessel provided with means for setting up a strong, substantially uniform magnetic field therethrough,

and containing electro-magnetic ion separating means. This last means comprises essentially an ion beam transmitter unit and an ion beam receiver. The transmitter unit comprises an ion source including an arc chamher into which the material whose isotopes are to be separated is introduced in vapor form, means for causing an arc to be present in said chamber, and accelerating electrodes cooperating with said are chamber to withdraw positive ions of the material and to project them in a beam transversely of the magnetic field. In accordance with well-understood principles, the ions follow arcuate paths and ions of different mass, after substantially 180 of arc, achieve both separation and in dependent concentration. The receiver may be effective to receive and retain one or more of the isotopes for subsequent removal. In some cases it is desirable to provide an electrostatic shield for the beam extending between the transmitter and receiver, the shield being termed herein a liner.

In the operation of a calutron, the tank or vessel is evacuated to a pressure on the order of 10" or 10'- mm. of Hg. Substantially higher pressures result in excessive scattering due to collisions between ions following the beam path and neutral atoms or molecules pres ent in the tank. However, as the pressure is reduced substantially below the critical pressure, irregularities and variations appear in the beam, adversely affecting the completeness of separation and the efficiency of collection. Under extreme conditions the beam may blow up completely. I

It is the basic conception in the present case that these beam irregularities or blowing up of the beam, are due to a deficiency of electrons or negative ions along the path of the beam, and that the operation of the calutron can be improved by providing a copious supply of electrons. The presence in a relatively heavy beam of a great number of positively charged ions in which the ions tend to repulse each other, produces a space charge condition which is partially neutralized by ionization of neutral atoms and molecules by collision and other causess A more complete space charge neutralization, and one which is efifective at comparatively reduced pressures, is brought about by special means supplying additional electrons to the vicinity of the ion beam.

In accordance with the present invention, the addiatent O Patented June 28, 1955 tional electrons are provided by irradiating the inner walls of the liner (or tank where no liner is used) with intense ultra-violet light. As a result of this irradiation photoelectrons are liberated from the walls, some of The electrons thus liberated have an energy of onlya few volts, and are confined to substantially straight line paths by the magnetic field. Actually the electron paths are tight spirals whose axes are parallel to the magnetic field. Hence, the most effective irradiation of the tank or liner walls occurs where projections of the beam in a direction parallel to the magnetic field intersect the said walls. Y I

With the foregoing general remarks in mind, it is an object of the present invention to effect improved space charge neutralization in a calutron.

It is a further object of the present invention to provide apparatus for supplying an increased amount of electrons for space charge neutralization of a calutron ion beam.

More specifically, it is a feature of the present invention to provide sources of radiation, particularly ultraviolet light, to irradiate tank or liner walls in order to liberate a copius supply of electrons.

Other objects will become apparent as the description proceeds, especially when taken in conjunction with the appended drawings, in which Figure l is a transverse section through a calutron embodying the present invention, and

Fig. 2 is a section on the line 22, Fig. 1. i

In this figure there is illustrated a calutron tank or vessel 10 preferably formed of steel, provided with a removable face plate 11 secured thereto by suitable fastening elements 12. Face plate 11 has openings 13 and 14 therethrough closed by removable panels 15 and 16 respectively, which are secured to face plate 11 by suitable fastening elements 17.

Panel 15 carries an ion source 20, comprising a block 21 having a vaporizing chamber 22 therein in which the charge material is heated and vaporized. The vapor passes through a port 23 into an arc chamber 24, in which an electric arc is present extending between a cathode 25 and an anode (not shown).

The forward face of the source 20 has an elongated opening therein partially closed by a pair of slit-defining plates 26. Spaced from and cooperating with said plates 26 are a pair of spaced accelerating electrodes 27. Electrodes 27 are maintained at a high negative potential with respect to plates 26, and serve to withdraw a stream of positive ions from arc chamber 24 and to project them at high velocity into the tank 10 in a direction transverse to the magnetic field. Source 20 and electrodes 27 together form a combination which is referred to herein as an ion beam transmitter. In Fig. 1, the numeral 30 designates one pole face of the magnets which set up a strong, generally parallel magnetic field normal to the plane of the paper in this figure.

It will be understood that either the source 20, including plates 26, or the accelerating electrodes27, may be grounded. In the illustrated embodiment, source 20 is grounded, and the accelerating electrodes 27 are carried at a high negative potential with respect to ground.

Due to the influence of the magnetic field, the ions projected through the slit between electrodes 27 follow Receiver 31 is located in the tank 10 so as to receive 1 and collect separated ions, and as shown is,provided 3 with separate pockets 32 and 33 respectively to receive and retain ions in the beams 28 and 29. Receiver 31 is supported on an insulator 34 carried by panel 16.

In order to prevent disturbance of the beams 28 and 29 by electrostatic fields set up between the tank walls and interior elements carried at electric potentials differing therefrom; a shield or liner 40, which may be formed of copper, is provided which is carried at the same high negative potential as the electrodes 27 and the receiver 31. It Will be understood that electrodes 27, liner 40, and receiver 31 are all electrically connected and are suitably insulated from the grounded tank 10 and source 20.

In order-to provide a copious supply of electrons within the liner 40 to effect a more complete space charge neutralization, there are provided one or more sources 50 of ultraviolet light, herein illustrated as three in number. It has been found that ordinary carbon arcs are entirely satisfactory. Ultraviolet light from these sources irradiates the interior walls of the liner 40, and results in freeing photoelectrons therefrom. The electrons freed from the side walls of the liner substantially in zones defined by projections of the beams 28 and 29 in the direction parallel to the magnetic field move toward the beam, and probably oscillate within the liner along paths parallel to the magnetic field. At all events, it has been conclusively demonstrated in actual practice that the supplying of copious amounts of electrons by irradiation of the inner walls of liner 40 (or the inner walls of tank 10 where no liner is employed) greatly improves beam stability, and permits operation at definitely lower tank pressures without causing the beams to blow up.

It is convenient to define the surfaces from which useful electrons are liberated, in accordance with the foregoing description as surfaces which are exposed to the beams of ions. By a surface exposed to the beams is meant a surface between which and the beams there is interposed no material barrier for the passage of liberated electrons from the surface to the beam. More specifically, the surfaces most effective for freeing electrons are those interior surfaces, whether of the tank or liner, which are exposed to the beams in directions parallel to the magnetic field.

Referring now to Fig. 2, we have shown a portion of tank 10, between pole faces 30 of the magnets, and the liner 40. One of the sources 50 of ultraviolet light is shown located inside the liner 4%) in position to irradiate its inner walls, and comprising spaced carbon electrodes 51 and 52.

While the arcs have been run with gaps between electrodes of three inches, best results have been obtained with a gap of between one and one-half, and two lVz-Z) inches. Various materials for the electrodes may be employed, but carbon in the form of a good quality of graphite is entirely satisfactory. To improve life of the source 50, the anode 51 is preferably made considerably larger in cross-section than the cathode 52. This prevents deep cratering of the anode.

While we have illustrated and described a specific form of calutron provided with carbon arcs serving as a source of ultravioletlight to irradiate the interior of the liner, it will be understood that this specific disclosure has been made merely to enable those skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What is claimed is:

1. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam, and carbon arc means disposed in said vessel effective to liberate electrons from interior metallic surfaces exposed to said ion beam.

2. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collcction of the ions in said beam; a metallic liner in said tank extending between said source and receiver through which said ion beam extends, and carbon arc means disposed in said liner effective to liberate electrons from the interior surface of said liner.

3. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam, a source of ultraviolet light in said vessel effective to irradiate interior metallic surfaces exposed to said ion beam.

4. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam; a metallic liner in said tank extending between said source and receiver through which said ion beam extends and a source of ultraviolet light in said liner effective to irradiate interior surfaces of said liner exposed to said beam.

5. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, and ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam, means in said vessel providing an electric are effective to irradiate interior metallic surfaces of said vessel exposed to said beam with ultraviolet light.

6. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam; a metallic liner in said tank extending between said source and receiver through which said ion beam extends, and means in said vessel providing an electric arc effective to irradiate interior surfaces of said liner with ultraviolet light.

7. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, and ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam, 21 carbon arc device in said vessel providing an electric are effective to irradiate interior metallic surfaces of said vessel exposed to said beam with ultraviolet light.

8. In a calutron, an evacuated vessel, magnet means for maintaining a magnetic field through said vessel, an ion transmitter and receiver in said vessel effective to transmit an ion beam transversely of said field from said transmitter to said receiver and to effect selective collection of the ions in said beam; a metallic liner in said tank extending between said source and receiver through which said ion beam extends, and a carbon arc device in said vessel providing an electric are effective to irradiate interior surfaces of said liner with ultraviolet light.

9. In an ion separating device comprising means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, carbon arc means disposed in said space for liberating a copious supply of electrons in said space tending to stabilize said beam.

10. In an ion separating device comprising means for projecting a relatively dense beam of positively charged ions through a hi hly evacuated space, metallic surfaces in said space exposed to said beam, and carbon arc means disposed adjacent said surface for liberating electrons from said surfaces.

11. In an ion separating device comprising means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, metallic surfaces in said space exposed to said beam, and means for irradiating said surfaces with ultraviolet light.

12. In an ion separating device comprising means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, metallic surfaces in said space exposed to said beam and an electric arc device for irradiating said surfaces with ultraviolet light.

13. in an ion separating device comprising means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, metallic surfaces in said space exposed to said beam and a carbon arc device for irradiating said surfaces with ultraviolet light.

14. In a device of the character described, means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, magnet means for maintaining a strong generally parallel magnetic field through said space, a metallic surface in said space exposed to said beam in a direction parallel to said magnetic field, and carbon are means disposed adjacent said surface for liberating electrons from said surface Where thus exposed to said beam.

15. In a device of the character described, means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, magnet means for maintaining a strong generally parallel magnetic field through said space, a metallic surface in said space exposed to said beam in a direction parallel to said magnetic field, and means for irradiating said surface where thus exposed to said beam with ultraviolet light.

16. In a device of the character described, means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, magnet means for maintaining a strong generally parallel magnetic field through said space, a metallic surface in said space exposed to said beam in a direction parallel to said magnetic field, and an electric are means for irradiating said surface Where thus exposed to said beam With ultraviolet light.

17. In a device of the character described, means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, magnet means for maintaining a strong generally parallel magnetic field through said space, a metallic surface in said space exposed to said beam in a direction parallel to said magnetic field, and a carbon are means for irradiating said surface Where thus exposed to said beam with ultraviolet light.

18. In a device of the character described, means for projecting a relatively dense beam of positively charged ions through a highly evacuated space, magnet means for maintaining a strong generally parallel magnetic field through said space, a metallic surface in said space exposed to said beam in a direction parallel to said magnetic field, and a carbon are means for irradiating said surface where thus exposed to said beam with ultraviolet light, said carbon are means comprising a cathode, and an anode considerably larger in cross-section than said cathode.

No references cited. 

1. IN A CALUTRON, AN EVACUATED VESSEL, MAGNET MEANS FOR MAINTAINING A MAGNETIC FIELD THROUGH SAID VESSEL, AND ION TRANSMITTER AND RECEIVER IN SAID VESSEL EFFECTIVE TO TRANSMIT AN ION BEAN TRANSVERSELY OF SAID FIELD FROM SAID TRANSMITTER TO SAID RECEIVER AND TO EFFECT SELECTIVE COLLECTION OF THE IONS IN SAID BEAM, AND CARBON ARC MEANS DISPOSED IN SAID VESSEL EFFECTIVE TO LIBERATE ELECTRONS FROM INTERIOR METALLIC SURFACES EXPOSED TO SAID ION BEAM. 